1. Field of the Invention
This invention relates to variable focus lens photographic cameras in general, and to such cameras having rangefinding means that are coupled to the lens of such a camera for lens focusing, in particular.
2. Description of the Prior Art
Photographic cameras incorporating variable focus lenses for focusing the image of a subject to be photographed at the film plane of such a camera are well known in the prior art. Apparatus included in such cameras for simultaneously determining the distance to a subject to be photographed and focusing said variable focus lens so that an in-focus image of said subject is formed at said film plane, are also well known in the prior art. Focusing apparatus of this type is generally referred to as a coupled rangefinder.
In order to properly focus the variable focus lens of a camera by means of a coupled rangefinder, a known relationship must exist between subject distance as determined by said rangefinder and the subject-in-focus position of said lens, to properly focus the image of a subject to be photographed at said camer's film plane. During manufacture, for example, the rangefinder and variable focus lens are normally assembled on the camera body without this relationship having first been established. However, this relationship is established later in the manufacturing cycle when it is more convenient and efficient to do so. The procedure for establishing this relationship is sometimes referred to as rangefinder to lens calibration.
A coupled rangefinder is normally linked to its associated variable focus lens through a mechanical coupling device such as a set of gears. Part of the normal rangefinder to variable focus lens calibration procedure involves the uncoupling of said rangefinder from said variable focus lens by unmeshing said gears so that each of these devices may be separately adjusted to the same subject distance or reference point in order to correlate rangefinder determined distance to variable focus lens position. Once each of these devices is so adjusted, they are recoupled to one another and are maintained in that position for subsequent rangefinder to variable focus lens focusing.
Arrangements for uncoupling a rangefinder from a variable focus lens so that said rangefinder and said lens may be calibrated with respect to one another have been disclosed in the prior art. In one such arrangement, which is described in U.S. Pat. No. 3,914,777 to Slavitter, the inventor of the present invention, an optical rangefinder is coupled, through a gearing arrangement, to a camer's variable focus lens. One of the gears in said gearing arrangement coupling said optical rangefinder to said variable focus lens is an idler gear that is normally meshed with two gears, one that rotates in response to rangefinder movement and one that rotates with said lens. In order to uncouple the rangefinder from its associated variable focus lens, a force is applied to said idler gear in a direction that is generally parallel to said idler gear's axis of rotation, against a biasing spring that normally maintains said idler gear in its fully engaged position. When fully depressed, the idler gear is disengaged from said rangefinder related gear and said lens gear so that the rangefinder and variable focus lens may be separately positioned. While this type of uncoupling arrangement is effective, it does have some inherent disadvantages. For example, in order to so axially move the idler gear, space must be provided adjacent said gear into which said gear can be moved. In many applications, it is not possible or feasible to provide the space that is necessary for this type of idler gear movement. In addition, if the gears that are normally meshed with the idler gear are the same width, and rotate in the same plane, said idler gear will become completely disengaged from both the rangefinder related gear and the lens gear when the rangefinder is uncoupled from its associated variable focus lens. In order to reengage these gears after calibration is complete, the teeth of the idler gear must be aligned with both the teeth of the rangefinder related gear and the teeth of the lens gear. If only one such alignment had to be made, it would be less difficult to recouple the rangefinder to the variable focus lens.
In the above-cited '777 patent to Slavitter, mention is made of a gear train coupling a rangefinder to a variable focus lens where said gear train includes an idler gear that is pivotable out of engagement with the rangefinder and variable focus lens related gears in order to uncouple said rangefinder from said variable focus lens. The idler gear is maintained in its engaged or coupled position by a spring force biasing means. A potential problem with this arrangement is the possibility of a reduction in the force transmitted by said spring biasing means if a change in the set of the spring portion of said spring force biasing means should occur, which could result in an unscheduled uncoupling of said rangefinder from said variable focus lens.